DESCRIPTION: (Applicant's Abstract) The broad objectives of this project are to develop a new subjective refraction instrument, evaluate its clinical performance, and develop strategies and procedures to exploit its unique capabilities. The instrument implements spherocylindrical powers in such a way that spherical and astigmatic powers are manipulated independently. That is, unlike conventional instruments, this instrument produces spherocylindrical power in three components that are mathematically orthogonal. This property offers important opportunities that could enhance the efficiency, accuracy, and reproducibility of this commonly performed clinical procedure. The instrument allows much greater flexibility in lens power changes. This invites investigation of a range of refraction protocols that have the potential to improve subjective refraction. Method of adjustment and other psychophysical procedures, such as maximum likelihood estimation, will be tested as clinical examination procedures in subjective refraction. The clinical performance of this instrument will be evaluated against conventional instrumentation, comparing repeatability, accuracy, and efficiency of subjective refraction. The feasibility of extending the technology to other environments in which subjective refraction is typically performed without phoroptors will be investigated. This includes evaluating this approach to astigmatic determination in trial lens refraction, and in combination with portable optometers.